THE OLD WOBLD MONKEYS 57
lobe of the right lung lies between it and the diaphragm below and behind. The apex is to the left of the sternum, and is usually formed by the left ventricle. The pericardium is considerably adherent to the diaphragm.
The aortic arch may give off its main branches as in Man, or there may be only two trunks—a left subclavian and an innominate artery, which breaks up into the right subclavian and both common carotid arteries. Sometimes intercostal arteries arise from the aortic arch.
In the arm the most important points to note are the presence of an arterial trunk which gives rise to the circumflex arteries. In some species the anterior humeral circumflex artery arises directly from the axillary trunk. The brachial artery is superficial to the median nerve, and bifurcates into radial and ulnar arteries in the arm.
The lingual and external maxillary arteries arise by a common trunk—a condition which also exists in the Chimpanzee,
In the leg the saphenous artery runs from the femoral artery to the dorsum of the foot.
There is no saphenous opening, and the intra-thoracic part of the vena cava inferior is shorter than in lower Primates.
Organs of Respiration.—In many species there is an air-sac communicating with the larynx between the epiglottis and thyroid cartilage, or through an opening in the epiglottis.
The tracheal rings are incomplete behind.
The left lung has two or three lobes, and the right lung